Modern radio transceivers often combine RF functions with digital circuitry. These mixed signal integrated circuits expand system capability and reduce cost, but present several design challenges.
One fundamental challenge facing mixed-signal systems is digital noise due to switching transients. It is impossible to prevent the noise from coupling through the substrate and package to sensitive analog designs. As a result, the noise unavoidably degrades radio transceiver performance. The power spectral density or spectrum of the digital switching noise usually appears at integer multiples of the data rate. Moreover, the noise typically increases at higher data rates.
In practice, the radio transceiver must support a wide range of RF channel frequencies, some of which occur near or at multiples of the digital data rate and coincident with the highest noise levels. The resulting problems tend to be more severe in narrowband systems, and it is not uncommon for this noise to degrade radio performance and cause failures. Accordingly, there is a need for new approaches to combat switching related noise.